Servo control of a lift apparatus and methods of use thereof

ABSTRACT

Disclosed herein are embodiments of a lift apparatus and systems containing a support and at least one lift apparatus for moving a substrate between the support and a transfer plane, using a servo-control system. Further disclosed herein are methods for servo control of a lift apparatus and lifting a substrate off of a support or lowering the substrate onto the support.

FIELD

The disclosure relates generally to the field of robotics and systemsand methods for servo control of a lift apparatus.

BACKGROUND

Semiconductor substrates are commonly processed in vacuum processingsystems. These systems include one or more chambers, each performingsubstrate processing operations such as etching, chemical vapordeposition or physical vapor deposition, which can include heating orcooling of the substrate, and a plasma to assist the process. Typically,the environment within such processing chambers is maintained at a lowsubatmospheric pressure. Each chamber includes inlets and outlets forevacuation apparatus and the admission of processing gases, as well asan aperture controlled by a slit valve to admit substrates. Suchprocessing chambers may be in communication with a substrate transferchamber, and the substrate transfer chamber may have a valve-controlledaperture through which substrates can be admitted from outside thesystem.

The transfer of a substrate to and from a chamber and to and from theoutside of the system is generally performed mechanically by a robot armat the end of which is a substrate retaining component (e.g., a blade orend effector). To facilitate sliding the blade end of the robot armunder the substrate, one or more lift pins lift the substrate about 20mm to 50 mm above the tool (e.g., a chuck assembly). The lift pins canbe pneumatic actuated. This is accomplished using full-stroke actuationwith solenoid valves such that the lift pins have two positions: up anddown. There may be a 30 mm to 40 mm distance between the up and downpositions of the lift pins. To transfer the substrate to the endeffector of the robot arm, the lift pins are extended to the up position(e.g., 20 mm to 40 mm), the end effector is positioned below thesubstrate, and the lift pins are lowered to the down position,transferring the substrate to the end effector in the process. The robotarm can then remove the substrate from the process chamber. However,this transfer process is inefficient because the substrate is extendedwell above the end effector, then well below the end effector, whichtakes time to complete.

Operating the lift pins with a full-stroke actuation also can causedamage to the substrate, particularly when the substrate is removed froma support such as an electrostatic chuck. After completion of processsteps, the pneumatic lift mechanism raises the lift pins to raise thesubstrate above the support so that the substrate can be removed fromthe chamber by the robot arm. When the support is an electrostaticchuck, before the lift pins can raise the substrate, the substrate mustbe “dechucked,” that is, the electrostatic force retaining the substrateon the chuck must be removed. Conventionally, the chucking voltagesupply is turned off and the chuck electrode and substrate are bothconnected to ground to remove the respective charges that accumulated onthe chuck electrode and substrate during application of the chuckingvoltage to the chuck electrode. However, this conventional dechuckingmethod may not succeed in removing all of the electrostatic attractiveforce between the substrate and the chuck before the lift pins attemptto lift the substrate from the chuck, and the substrate can stick to thechuck. Upon actuation of the lift pins, the substrate can crack or breakand/or pop off the chuck into a position from which it is difficult toretrieve and align properly by a substrate transfer robot. In someinstances, the robot arm collides with the misaligned substrate causingfurther damage to the robot arm. Substrate sticking can occur even whenthe support is not an electrostatic chuck, for example, when the supportis a pedestal having a build-up of sputter material causing adherence ofthe substrate. All of these problems can lead to process downtime andcapital costs for repairing the apparatus.

BRIEF SUMMARY

According to embodiments, described herein is a lift apparatus fortransferring a substrate between a support and a transfer plane, thelift apparatus comprising: a lift pin assembly, comprising: a lift pinconfigured to move the substrate between the support and the transferplane; at least one pneumatic actuator comprising a moving memberconfigured to provide a load to the lift pin; at least one proportionalpneumatic valve configured to control fluid flow between the at leastone pneumatic actuator and a pressurized fluid supply or a vent; aplurality of pressure sensors each configured to independently measurepressure in a respective supply line to the at least one pneumaticactuator; and at least one position sensor configured to measure aposition of the member; and a servo-control system in communication withthe lift pin assembly.

According to embodiments, further described herein is a method,comprising: receiving by a controller a first pressure measurement froma first pressure sensor that measures pressure in a first chamber of apneumatic actuator; receiving by the controller a second pressuremeasurement from a second pressure sensor that measures pressure in asecond chamber of the pneumatic actuator; receiving by the controller aposition measurement from a position sensor that measures a position ofa moving member of the pneumatic actuator; generating a control signalbased on the first pressure measurement, the second pressure measurementand the position measurement; transmitting the control signal to atleast one proportional pneumatic valve of a servo-control system tocontrol pressurized fluid to the pneumatic actuator; and operating theservo-control system to extend at least one lift pin and lift asubstrate off of a support via the at least one lift pin.

According to various embodiments, further described herein is a methodcomprising: operating a servo-control system to lift a substrate off ofa substrate support, wherein the servo-control system is configured tocontrol a lift pin assembly for lifting the substrate, comprising:actuating at least one proportional pneumatic valve to permit gas toflow through a first gas line into a first chamber of a pneumaticactuator of the lift pin assembly and through a second gas line into asecond chamber of the pneumatic actuator; measuring pressure in thefirst gas line with a first pressure sensor and measuring pressure inthe second gas line with a second pressure sensor; measuring position ofa moving member of the pneumatic actuator with a position sensor;controlling the at least one proportional pneumatic valve with theservo-control system to apply a contact force of about 2 N to about 10 Nby the moving member to the substrate; and lifting the substrate off ofthe support by a lift pin operable to receive a load by the movingmember.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings in which likereferences indicate similar elements.

FIG. 1 depicts a processing chamber that includes a lift pin assembly.

FIG. 2 depicts a lift pin assembly according to various embodiments.

FIG. 3 depicts a lift pin according to various embodiments.

FIG. 4 depicts a lift pin according to various embodiments.

FIG. 5 depicts a servo control system according to embodiments.

FIG. 6 illustrates a method for transferring a substrate between asupport and a transfer chamber according to various embodiments.

FIG. 7 illustrates a method of controlling a lift apparatus using aservo-control system according to various embodiments.

FIG. 8 illustrates a method of transferring a substrate from a processchamber to a transfer chamber using a robot arm in communication with aservo-controlled lift pin assembly according to various embodiments.

DETAILED DESCRIPTION

Reference throughout this specification to, for example, “oneembodiment,” “certain embodiments,” “one or more embodiments” or “anembodiment” means that a particular feature, structure, material, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the disclosure. Thus, the appearances ofthe phrases such as “in one or more embodiments,” “in certainembodiments,” “in one embodiment” or “in an embodiment” in variousplaces throughout this specification are not necessarily referring tothe same embodiment of the disclosure. Furthermore, the particularfeatures, structures, materials, or characteristics may be combined inany suitable manner in one or more embodiments.

As used herein, the singular forms “a,” “an,” and “the” include pluralreferences unless the context clearly indicates otherwise. Thus, forexample, reference to “a lift pin” includes a single lift pin as well asmore than one lift pin.

As used herein, the term “about” in connection with a measured quantity,refers to the normal variations in that measured quantity as expected byone of ordinary skill in the art in making the measurement andexercising a level of care commensurate with the objective ofmeasurement and the precision of the measuring equipment. In certainembodiments, the term “about” includes the recited number±10%, such that“about 10” would include from 9 to 11.

The term “at least about” in connection with a measured quantity refersto the normal variations in the measured quantity, as expected by one ofordinary skill in the art in making the measurement and exercising alevel of care commensurate with the objective of measurement andprecisions of the measuring equipment and any quantities higher thanthat. In certain embodiments, the term “at least about” includes therecited number minus 10% and any quantity that is higher such that “atleast about 10” would include 9 and anything greater than 9. This termcan also be expressed as “about 10 or more.” Similarly, the term “lessthan about” typically includes the recited number plus 10% and anyquantity that is lower such that “less than about 10” would include 11and anything less than 11. This term can also be expressed as “about 10or less.”

Unless otherwise indicated, all parts and percentages are by weight.Weight percent (wt. %), if not otherwise indicated, is based on anentire composition free of any volatiles, that is, based on dry solidscontent. The servo-controlled lift apparatus will be discussed in thecontext of a lifting mechanism for a support (e.g., a chuck, anelectrostatic chuck, a pedestal, and so on). However, those of ordinaryskill in the art will recognize that the servo-controlled lift apparatuscan be used in systems comprising any processing chamber (e.g., asemiconductor processing chamber) that includes a lifting mechanism totransfer a substrate from the chamber to a robot arm and/or from therobot arm to the chamber.

Conventional lift mechanisms use an on/off pneumatic valve with manualrestrictors to control velocity of the pneumatic cylinder (also referredto herein as a pneumatic actuator). Cylinder position is monitored onlywith digital end position sensors and compressed air delivery to thecylinder is switched by a solenoid driven spool valve. In the context ofan electrostatic chuck assembly, energy release of a substrate is notalways consistent, which can lead to substrate breakage if the pneumaticactuator force output of the lift pin is higher than the substratestrength. In some circumstances the substrate is displaced, which canresult in collision of the substrate with the robot art causingsubstrate breakage and/or damage to the robot arm. There is no trackingor feedback of the lift pin position in these lift mechanisms making itunclear as to what caused the failure. Conventional lift mechanisms alsolimit throughput because the pneumatic actuator must move the lift pinsslowly enough to be safe for substrate contact, but it takes 2-8 secondsfor the lift pins to move.

A lift apparatus according to embodiments herein includes a positionsensor that monitors the position of the pneumatic cylinder throughoutthe stroke. The lift apparatus further includes a proportional pressurecontrol valve with pressure feedback from both sides of the pneumaticcylinder. This could be implemented with a single 5/2 spool valve styleproportional valve or by two separate pressure control proportionalvalves. Each side of the pneumatic cylinder includes a pressure sensor.The proportional pressure control valve allows a varying flow andpressure to be controlled on each side of the pneumatic cylinder. Alsoincluded in the lift apparatus is a first position sensor that sends asignal to the controller regarding the position of the cylinder. Oncethese sensors are available, then the controller can control the forceoutput by adjusting the delta pressure between the two sides, controlthe position by monitoring the position feedback, and control thestiffness by adjusting the average pressure between the two sides. Theoverall system stiffness is driven by the mass of gas behind each sideof the cylinder.

With this control, the cylinder can be moved and stopped at intermediatepositions within the full stroke length, move time can be controlled andsubstrate sticking to a support (e.g., a chuck assembly) can be sensed.Additionally, the lift apparatus, according to embodiments herein,enables faster lift pin motion, which can increase system throughput.The lift apparatus can also control force output, which can keep thesubstrate from breaking if the support (e.g., electrostatic chuck) failsto release. The lift apparatus further enables faster substrate transferto the robot blade because the lift motion can be shortened (e.g., thetotal stroke of the lift is 38 mm, but it only takes 10 mm of motion totransfer the substrate to the blade). Position control of the lift pinsalso can be controlled, which enables a new substrate edge cleaning stepto remove polymer deposition that occurs during the etch step. Forexample, the substrate could be lifted off a support surface by just 1mm and could then be cleaned.

In reference to FIG. 1, during operation of a process chamber 100, arobot arm (not shown) moves a substrate 101 into the chamber 100 througha slit valve 106. The robot arm places the substrate on the tips of thelift pins 142, which are elevated by a pneumatic lift mechanism 146above the top of the support 110 (e.g., an electrostatic chuck). Thepneumatic lift mechanism 146, under control of a computer control system162, then lowers the lift pins 142 so that the substrate is positionedonto the surface of the support. The pneumatic lift mechanism 146 mayinclude at least one lift pin assembly comprising at least one pneumaticactuator and a servo-control system in fluid communication with the atleast one pneumatic actuator, the servo-control system comprising atleast one proportional pneumatic valve, a plurality of pressure sensorsand at least one position sensor.

According to embodiments, a servo controlled lift apparatus systemaccording to embodiments herein can include a support (e.g., a chuckassembly) and a lift apparatus for transferring a substrate between thesupport and a transfer chamber. The lift apparatus can comprise a liftpin assembly, comprising at least one pneumatic actuator, at least oneproportional pneumatic valve, a plurality of pressure sensors, at leastone position sensor, and a servo-control system in communication withthe lift pin assembly.

Once the lift pins have lowered the substrate 101 onto the support 110,a process may begin, which can be an etch process, deposition process,cleaning process, and so on. The process may include initiating aplasma. According to certain embodiments, when the support is anelectrostatic chuck, the computer control system 162 can apply a DCchucking voltage to a chuck 110 and may apply a heat transfer gas to asubstrate-to-chuck interface. The chucking voltage causes negative andpositive charges to accumulate on the facing surfaces of the substrate101 and the chuck electrode 104, respectively.

The chuck 110 may include an upper dielectric (e.g., an electrostaticpuck), which may support the substrate 101. After the substrate 101 ispositioned onto the upper dielectric of the support 110, the lift pins142 continue to descend into a pedestal 114. When the support 110 is anelectrostatic chuck, the opposite polarity charges on the substrate 101and chuck electrode 104 produce an electrostatic attractive force, whichpresses the substrate 101 against the upper face of the chuck 110. Thechucking voltage is set to a value high enough to produce anelectrostatic force between the substrate 101 and the chuck 110 which isadequate to prevent substrate movement during subsequent process stepswithin the process chamber 100. The substrate 101 thus retained securelyon the chuck 110 is referred to as being “chucked.”

After the substrate is placed on the support 110 (e.g., chucked), one ormore process steps are performed in the chamber 100, such as depositionor etching films on the substrate 101. For processes that employ plasma,an RF power supply 130 selectively applies RF power to an antenna 112and between a cathode pedestal 114 and a grounded anode 104, whichgenerates a plasma 103 in the region above the substrate 101. The plasma103 provides an electrically conductive path between the substrate andground. However, because of the difference between the mobilities ofelectrons and positive ions, a DC voltage drop appears across the plasma103 so that the substrate 101 is biased negative relative to ground. Ifthe chucking voltage applied to the chuck electrode (the pedestal) 114by the DC voltage supply 120 is positive, the total DC voltage betweenthe substrate 101 and the chuck electrode 114 will be the sum of thesubstrate bias and the chucking voltage, thus, the substrate biasincreases the electrostatic force retaining the substrate 101.

The lift assembly may include three lift pins 142 mounted on a carriage140 that are raised and lowered by the pneumatic lift mechanism 146.After completion of the process steps, the pneumatic lift mechanism 146raises the lift pins 142 to raise the substrate 101 above the support110 so that the substrate 101 can be removed from the chamber 100 viathe robot arm (not shown).

In embodiments where the support 110 is an electrostatic chuck, beforethe lift pins 142 can raise the substrate 101, the substrate 101 shouldbe electrically dechucked, that is, the electrostatic force retainingthe substrate 101 on the chuck should be removed or canceled. Thechucking voltage supply is turned off, and the chuck electrode 114 andthe substrate 101 are both connected to ground so as to remove therespective charges that accumulated on the chuck electrode 114 and thesubstrate 101 during the previous application of the chucking voltage tothe chuck electrode 114. The substrate may be grounded by leaving the RFpower supply 130 on at a reduced power level to maintain a plasma 103,which provides an electrically-conductive path from the substrate 101 tothe grounded walls of the chamber 100. However, as discussed above,after a dechucking method is used, a residual charge often still remainson the substrate 101 and chuck 110 due to charge migration and/or fieldemission charging. As such, standard dechucking methods may cause unduephysical force to dislodge the substrate from the chuck. In some cases,using conventional dechucking methods and conventional lift pinassemblies, the substrate cracks and/or breaks or is only partiallyremoved. Under the latter circumstance, when the robot arm moves in toretrieve the partially removed substrate, the robot arm can crash intothe substrate causing damage not only to the substrate, but to the robotarm resulting in equipment downtime. It should be noted that inembodiments where the support 110 is not an electrostatic chuck,sticking issues can still arise. For example, material deposited on thesupport from a sputtering process may cause sticking of the substrate tothe support. The lift apparatus and control systems described herein cansafely remove a substrate from any support without cracking or breakingthe substrate.

Servo controlled lift apparatus systems as described herein provide theability to sense and control force, position and stiffness of apneumatic control valve. The systems also enable faster lift pin motion,which can increase system throughput and control of force output thatcan keep the substrate from breaking if a substrate sticks to thesupport or, for example, if an electrostatic chuck fails to release. Thesystems enable faster substrate transfer to the robot blade because thelift motion can be shortened and position control of the lift pins,which can enable a new substrate edge cleaning step to remove polymerdeposition that occurs during the etch step.

A lift pin assembly 200 (for each lift pin) according to one embodimentof the present disclosure is shown in FIG. 2. The lift pin assembly 200includes a low friction air cylinder 202 having a glass bore and agraphite seal. A sleeve 204 is positioned over a shaft of the cylinder202 and serves as a low position hard stop for the lift pin 214. Alsoattached to the shaft of the cylinder 202 is a ball joint 206 thatenables the lift pin assembly 200 to align with other lift pinassemblies while holding a substrate. The lift pin assembly 200 canfurther include a linear slide 208 along which a slide carriage 210moves in a vertical direction. The linear slide 208 is attached to alift assembly bracket 212. The lift pin 214 extends into the processchamber through a bellows 216, which permits vertical movement of thelift pin 214 while maintaining a vacuum in the chamber.

As discussed above, the transfer of a substrate is accomplishedmechanically by means of a robot arm at the end of which is a substrateretaining component such as an end effector or robot blade. One type ofretaining component is a flat blade through which a vacuum channel isformed, terminating in an outlet. The blade can pick up a substrate bytouching the upper surface of the blade to the bottom surface of thesubstrate and optionally applying a vacuum to cause the substrate tostick to the blade. An advantage of the flat blade is that it is flatand thin and can be easily maneuvered between the tight spaces of asubstrate storage cassette to pick up a substrate.

Another type of substrate retaining means has a shoe attached to therobot arm. The shoe may be a tray-like extension at the leading end ofthe arm, with a bevelled contour shaped to accommodate a substrate. Theshoe helps to engage the substrate and retain the substrate in placeupon the arm while the robot arm swings around to deliver the substrateto another location.

FIG. 3 shows an embodiment of a lift pin assembly 300 in accordance withthe embodiments of the present disclosure. At least one lift pinassembly 300 may be a part of a lift apparatus for transferring asubstrate between a support and a transfer plane (e.g., into a transferchamber). The lift pin assembly 300 may include a four (4) wayproportional pneumatic valve 301 supplied by a main source ofpressurized fluid (e.g., air) 302. The proportional pneumatic valve 301can include a pair of springs 303, 304 that enable movement of anactuator between each of four (4) flow paths 305, 306, 307, 308. Flowpaths 305 and 308 permit pressurized gas to flow from the source 302 andinto lines 309 and 310, respectively. Flow paths 306 and 307 permit gasto vent through lines 311 and 312, respectively.

The lift pin assembly 300 further includes pressure sensors 313, 314,which measure the gas pressure in chambers 315, 316, respectively, of apneumatic actuator 317. Each pressure sensor may be a diaphragm typesensor with a strain gauge, e.g., a resistance wire strain gauge, and/orpiezoresistive strain gauge. According to embodiments, the proportionalpressure control valve can be a single 5/2 spool valve styleproportional valve or by two separate pressure control proportionalvalves. In at least one embodiment, the pressure sensor is aproportional pressure regulator with piezo technology. Chambers 315 and316 are defined on each side of a moving member (e.g., a piston) 318 andby the interior of a cylinder housing 319 of the pneumatic actuator 317.The proportional pneumatic valve 301 permits pressurized gas to flowinto and/or to vent from chambers 315, 316. The lift pin assembly 300may also include a position sensor 320 that determines the position ofthe moving member 318 within the pneumatic actuator 317. The positionsensor can be a linear position sensor and/or an inductive positionsensor, for example, a magneto-inductive position sensor. The movingmember 318 controls the position of the lift pin 321.

During operation, the lift pin 321 has a load 322 that may be acombination of the weight of a substrate (not shown), a spring forcefrom a bellows and/or pressure inside the process chamber. According toembodiments, the lift pin assembly 300 may also include one or more balljoint (not shown) to help align with other lift pin assemblies in thelift apparatus.

Another embodiment of a lift pin assembly 400 in accordance with thedisclosure is shown in FIG. 4. At least one lift pin assembly 400 may bea part of a lift apparatus for transferring a substrate between asupport and a transfer plane associated with a transfer chamber. Thelift pin assembly 400 may include two 2-way proportional pneumaticvalves 401A, 401B supplied by one (shown) or more main source ofpressurized fluid (e.g., air) 402. Each of the pneumatic valves 401includes a spring 403, 404 that enables movement of the actuator betweeneach of flow path 405, 406, 407, 408. Flow paths 405 and 408 permitpressurized gas to flow from the source 402 and into lines 409 and 410,respectively. Flow paths 306 and 307 permit gas to vent through lines411 and 412, respectively.

The lift pin assembly 400 further includes pressure sensors 413, 414,which measure the gas pressure in chambers 415, 416, respectively, of apneumatic actuator 417. Chambers 415 and 416 are defined on each side ofa moving member (e.g., a piston) 418 and by the interior of a cylinderhousing 419 of the pneumatic actuator 417. The proportional pneumaticvalves 401A, 401B permit pressurized gas to flow into and/or to ventfrom chambers 415, 416. The lift pin assembly 300 may also include aposition sensor 420 that determines the position of the moving member418 within the pneumatic actuator 417. The moving member 418 controlsthe position of the lift pin 421. During operation, the lift pin 421 hasa load 422 that may be a combination of the weight of a substrate (notshown), a spring force from a bellows and/or pressure inside the processchamber. According to embodiments, the lift pin assembly 400 may alsoinclude one or more ball joint (not shown) to help align with other liftpin assemblies in the lift apparatus.

The above-mentioned lift assembly 300, 400 can be a part of aservo-control system. The servo control system initiates the pneumaticvalve(s) 301, 401A, 401B to direct pressurized gas into chambers 315,315, 415, 416 and/or to vent pressurized gas from these chambers. Theservo control system utilizes measurements from the pressure sensors313, 314, 413, 414 and the position sensor 320, 420 to determine theoutput force of the pneumatic actuator 317, 417 and the stiffness of thevalves(s) 301, 401A, 401B. A controller (not shown), in addition to thelift pin assembly 300, 400, completes the servo control system. Theservo-control system is configured to maintain a closed loop, wherein atleast one of chamber pressure and moving member position is controlledwithin the pneumatic actuator. The at least one proportional pneumaticvalve 301, 401A, 401B is configured to direct pressurized fluid 302, 402through at least one of the plurality of fluid flow paths 305, 306, 307,308 in response to a control signal from the servo-control system. Thecontroller calculates the proper amount of pressure for each pneumaticcylinder chamber to move the lift as fast as possible while avoiding thesubstrate damage.

FIG. 5 shows a servo control system 500 in accordance with embodimentsherein. The path planner 502 generates a trajectory (y_(cmd)) to move alift pin close to a substrate. The position controller 504 produces thecommanded force (f_(cmd)) that is required to move the lift pin assembly514 based on the generated trajectory and the received feedback (y) fromthe position sensor. The force estimator's 506 function is to determineif contact between the support and the substrate has occurred or not andwhether the support is engaged or released. From the estimated force(f_(e)) of the force estimator 506, the force controller 508 commandsthe path planner 502 whether to continue the movement or to pause untilthe support (e.g., electrostatic chuck) is fully disengaged whilekeeping a small amount of force to push the substrate without breakingit. The force controller 508 receives two inputs: the commanded force(f_(cmd)) from the position controller 504 and the estimated force(f_(e)) from the force estimator 506. It calculates the right amount offorce (f_(d)) to keep the contact force between the lift pin and thesubstrate below a certain limit (i.e., to prevent breaking thesubstrate) and to maintain the position of the lift pin close to thesubstrate. The pressure controller 510 calculates the commanded pressurefor each chamber of the pneumatic actuator 512 based on the requiredforce (f_(d)) that it receives from the force controller 508. Thepressure controller 510 in effect produces the right amount of force tomove the lift pin while preventing the substrate from breaking. Thepneumatic actuator 512 produces the desired force output (f) to move theat least one lift pin or to maintain contact with the substratedepending on the amount of the chamber pressures p₁ and p₂. It should benoted that each of the position controller 504, force estimator 506,force controller 508 and pressure controller 510 may be modules of acontroller of the servo-control system or each may be an individualcontroller.

In one embodiment, servo-control of the lift apparatus can beimplemented via a control algorithm for controlling the lift apparatus.For example, a pneumatic actuator 317, 417 of the lift apparatus caninclude a pneumatic cylinder. See FIGS. 3 and 4. The difference betweenthe pressures P_(a), P_(b) in the chambers 315, 316, 415, 416 determinesthe output force F and their sum governs the desired stiffness of thecylinder 318, 418. Thus, in order to control the force and stiffness ofthe pneumatic actuator 317, 417 one has to be able to control thepressures P_(a), V_(a), A_(a) and P_(b), V_(b), A_(b) of the cylinderchambers 315, 316, 415, 416 individually.

The relationship between the pressure in each chamber P_(a), V_(a),A_(a) and P_(b), V_(b), A_(b), the air mass flow rate {dot over(m)}_(a), {dot over (m)}_(b), and the piston position ±x. Each chamber315, 316, 415, 416 can be modeled as a control volume with the followingassumptions: 1) the air is an ideal gas, 2) pressure and temperaturewithin each chamber are uniformly distributed, and 3) the kinetic andpotential energy of the air are negligible. Considering theseassumptions and applying the conservation of mass, the ideal gas model,and the conservation of energy to each chamber, we obtain Equation (1):

$\begin{matrix}{\overset{.}{P} = {\frac{RT}{V}\overset{.}{m}}} & (1)\end{matrix}$

where R is the ideal gas constant, P is the pressure, T is the absolutetemperature, V is the volume, and {dot over (m)} is the mass flow ratein or out of the cylinder chamber 315, 316, 415, 416. The volume of eachchamber depends on piston position as in Equation (2):

V=V ₀ +A(½L±x _(p))  (2)

where V₀ is the inactive volume at the end of the stroke and includesthe volume V_(a), V_(b) of the tube connecting the chamber 315, 316,415, 416 to the pressure sensor, A is the effective piston area, L isthe piston stroke, and x_(p) is the piston position. The normalizedinactive length associated with the inactive volume V_(a), V_(b) in eachchamber 315, 316, 415, 416 of the cylinder 318, 418 can be defined asL_(oa)=V_(oa)/A_(a), and L_(ob)=V_(ob)/A_(b), where a and b denote thetwo chambers 315, 316, 415, 416 of the cylinder as shown in FIGS. 3 and4. Therefore, the volume of each chamber as a function of the pistonposition will be as shown in Equation (3):

V _(a,b) =A _(a,b)(L _(a,b) ±x _(p)), L _(a,b) =L _(oa,ob)+½L  (3)

In Equations (2) and (3), the plus and minus signs correspond tochambers a and b, respectively. Combining Equations (1) and (3), thepressure equations of the chambers become

$\begin{matrix}\{ \begin{matrix}{{\overset{.}{P}}_{a} = {{\frac{RT}{V_{a}}{\overset{.}{m}}_{a}} - {\frac{P_{a}}{L_{a} + x_{p}}{\overset{.}{x}}_{p}}}} \\{{\overset{.}{P}}_{b} = {{\frac{RT}{V_{b}}{\overset{.}{m}}_{b}} - {\frac{P_{b}}{L_{b} + x_{p}}{\overset{.}{x}}_{p}}}}\end{matrix}  & (4)\end{matrix}$

An isothermal approximation for the chamber charging/discharging processcan be used with good results. Nevertheless, to compensate for theisothermal process assumption, the controller should be designed robustagainst parametric uncertainty. The force produced by the pneumaticcylinder is as shown in Equation (5):

F=P _(a) A _(a) −P _(b) A _(b) −P _(atm) A _(r)  (5)

where A_(r) is the cylinder rod cross-sectional area and P_(atm) is theatmospheric pressure. The stiffness of the cylinder is the rate ofchange of the cylinder force F with respect to the piston position x,with the mass of air inside the chambers, m_(a,b), considered constantas follows in Equation (6):

$\begin{matrix}{K = {- \frac{\delta\; F}{\delta\; x_{p}}}} & (6)\end{matrix}$

Using force from (5) into (6) we get Equation (7):

$\begin{matrix}{K = {{{- A_{a}}\frac{\partial P_{a}}{\delta\; x_{p}}} + {A_{b}\frac{\partial P_{b}}{\delta\; x_{p}}}}} & (7)\end{matrix}$

Assuming constant temperature, the pressure in each chamber will be afunction of the mass of the air inside the chamber (m) and the positionof the piston (x_(p)). The time derivative of the pressure becomesEquation (8):

$\begin{matrix}{\frac{dP}{dT} = {{\frac{\delta\; p}{\delta\; m}\overset{.}{m}} + {\frac{\delta\; p}{\delta\; x_{p}}{\overset{.}{x}}_{p}}}} & (8)\end{matrix}$

Comparing (4) and (8), the partial derivative of the pressure withrespect to position is

$\begin{matrix}\{ \begin{matrix}{\frac{\delta\; P_{a}}{\delta\; x_{p}} = \frac{P_{a}}{L_{a} + x_{p}}} \\{\frac{\delta\; P_{b}}{\delta\; x_{p}} = \frac{P_{b}}{L_{b} - x_{p}}}\end{matrix}  & (9)\end{matrix}$

From (7) and (9), the actuator stiffness can be written as

$\begin{matrix}{K = {\frac{A_{a}P_{a}}{L_{a} + x_{p}} + \frac{A_{b}P_{b}}{L_{b} - x_{p}}}} & (10)\end{matrix}$

The lift pin assemblies 300, 400 as described above, can be used in aprocess chamber as part of the servo control system to remove (e.g.,dechuck) at least one substrate from a support (e.g., an electrostaticchuck assembly).

The servo controlled lift apparatus according to embodiments herein candetermine the position of the at least one lift pin 321, 421 uponreceiving a signal indicative of cylinder 318, 418 position (x) from theposition sensor 320, 420. The position of the at least one lift pin 321,421 also is indicative of the position of a substrate received by the atleast one life pin 321, 421. For example, the position of the at leastone lift pin 321, 421 coupled with the predetermined thickness of thesubstrate enables a precise determination of the substrate's position inthe process chamber.

The servo controlled lift apparatus, according to embodiments herein,enables determination of the force F produced by the pneumatic cylinder.See Equation (5). According to embodiments, if the servo control systemdetermines that the positive force F (e.g., when the lift pin is rising)reaches a predetermined value, for example, a relatively high outputforce indicative of a substrate sticking to a support, the system canslow down or reverse movement of the lift pin by reducing (e.g., at alinear rate, an exponential rate) the pressure P_(a) in chamber 315, 415and/or increasing pressure P_(b) in chamber 316, 416. Practically,substrates that stick to supports can be peeled off. Servo control ofthe lift apparatus as described herein can slowly increase or reduceoutput force to prevent breaking the substrate and/or to slowly peel thesubstrate off the support assembly.

Also disclosed herein are methods for controlling a lift apparatus, asdescribed above, associated with a process chamber. FIG. 6 refers to aprocess 600 for transferring a substrate between a process chamber and atransfer plane associated with a transfer chamber. After completion ofsubstrate processing at block 602, at block 604 the substrate isdischarged from the semiconductor process chamber (e.g., discharged froma support). At block 606, the lift pins are actuated to clear thesubstrate from the support. As described above, a servo control systemcontrols the lift apparatus and can determine the position of thesubstrate as well as the force output of the pneumatic cylinder(s).According to embodiments, the servo control system can control the speedof the lift pin(s) and can control how high and/or low to raise the liftpin(s). The servo control system can also control the force output ofthe cylinder, by independently controlling the pressure in each chamberof the pneumatic control valve, to avoid applying excessive forcecausing breakage of the substrate. At block 608, the robot arm isactivated to grasp the substrate from the lift pin assembly. Asdiscussed above, the robot arm can move just high enough to clear thelift pin assembly. At block 610, the robot arm removes the substratefrom the process chamber system. Once the substrate is received, therobot arm may transfer the substrate into the transfer chamber. At block612, if the system receives a signal to process another substrate by thesemiconductor chamber, the robot arm positions the new substrate forprocessing on the lift pins at block 614. At block 616 the lift pins arelowered together with the substrate to place the substrate on thesupport.

Referring to FIG. 7, according to embodiments, the method 700 caninclude at block 702 receiving, by a controller, a first pressuremeasurement from a first pressure sensor that measures pressure in afirst chamber of a pneumatic actuator. The controller may be a computingdevice such as a programmable logic controller, system on a chip (SoC),and so on. The method can further include at block 704 receiving by thecontroller, a second pressure measurement from a second pressure sensorthat measures pressure in a second chamber of the pneumatic actuator. Atblock 706, the method can include receiving by the controller a positionmeasurement from a position sensor that measures a position of a movingmember (e.g., cylinder) of the pneumatic actuator. At block 708, themethod can include generating a control signal based on the firstpressure measurement, the second pressure measurement, the positionmeasurement, and the maximum acceptable contact force between thesubstrate and the lift mechanism. At block 710 the method can includetransmitting the control signal to at least one proportional pneumaticvalve of a servo-control system to control pressurized fluid to thepneumatic actuator. At block 712, the method can include operating theservo-control system to extend at least one lift pin and lift asubstrate off of a support via the at least one lift pin. According toembodiments, the method may further include transferring the substratefrom the at least one lift pin to a transfer plane and into a transferchamber using a robot arm.

According to embodiments, the controller can determine the differencebetween the first pressure measurement and the second pressuremeasurement to determine an output force of the pneumatic proportionalvalve. In one embodiment, the controller adds the first pressuremeasurement to the second pressure measurement to determine a stiffnessof the pneumatic proportional valve. The stiffness can be set to a highamount to make the control system more robust against the stiction inthe lift mechanism. In response to the output force, the stiffness andthe position of the moving member, the controller can control the atleast one pneumatic actuator to move the lift mechanism up whilepreventing the breaking of the substrate.

FIG. 8 illustrates a method 800 of operating a servo-control system tolift a substrate off of a substrate support. In accordance withembodiments described herein, the servo-control system is configured tocontrol a lift pin assembly for lifting the substrate. The method 800can include at block 802, actuating at least one proportional pneumaticvalve to permit gas to flow through a first gas line into (or vent) afirst chamber of a pneumatic actuator of the lift pin assembly andthrough a second gas line into (or vent) a second chamber of thepneumatic actuator. As discussed herein, in embodiments the lift pinassembly can include, for example, two proportional pneumatic valves. Afirst of the valves can control pressure in the first gas line and asecond of the valves can control pressure in the second gas line andboth valves may be controlled by the servo-control system. The at leastone proportional pneumatic valve may also include a vent to releasepressure in the gas supply lines as may be needed to balance pressurebetween the first chamber and the second chamber and to achieve adesired force output or contact force of the at least one lift pinagainst the substrate.

The method 800 may further include at block 804, measuring pressure inthe first gas line with a first pressure sensor and measuring pressurein the second gas line with a second pressure sensor. Each pressuresensor may be located at any point in the line between the at least oneproportional pneumatic valve and the pneumatic actuator. In embodiments,each pressure sensor may be positioned and operable to measure thepressure at the inlet of each chamber of the pneumatic actuator.

The method 800 may further include at block 806 measuring the positionof the moving member (e.g., the piston connected to the lift pin) of thepneumatic actuator with a position sensor. As shown in FIGS. 3 and 4,when the moving member is positioned at approximately the middle of thepneumatic actuator the position is x=0. If the moving member moves awayfrom the substrate (e.g., downward), then the moving member moves in anegative direction (−x). If the moving member moves toward the substrate(e.g., upward), then the moving member moves in a positive direction(+x).

The method 800 further can include a block 808, controlling the at leastone pneumatic actuator with the servo-control system to apply a contactforce of about 2 N to about 10 N by the moving member to the substrate.When the moving member, which comprises the lift pin, contacts thesubstrate to lift the substrate off of the support, the force applied bythe moving member to the substrate is controlled to about 2 N to about10 N to avoid breaking or cracking the substrate. The servo-controlsystem will actuate the at least one proportional pneumatic valve toincrease, decrease or maintain the pressure supplied to (or in) each ofthe chambers of the pneumatic actuator. According to embodiments, thepressure supplied to each chamber may be independently controlled by aplurality of proportional pneumatic valves. For example, the pressurep_(A) in the first chamber may be increased, while the pressure p_(B) inthe second chamber is decreased (e.g., vented). If the servo-controlsystem determines that moving the moving member will cause the contactforce on the substrate to exceed about 2 N to about 10 N, for example,about 2 N, about 3 N, about 4 N, about 5 N, about 6 N, about 7 N, about8 N, about 9 N, or about 10 N, then the servo-control system willdetermine that the wafer is sticking and will actuate the at least oneproportional pneumatic valve to maintain the pressure in each of thechambers. This applies a constant force to the substrate that will, forexample, peel the substrate off of the support, but without cracking orbreaking the substrate.

The method 800 further includes at block 810 lifting the substrate offof the support by the moving member. As discussed above, the movingmember will move and apply a contact force of about 2 N to about 10 N tothe substrate. The moving member may move in a negative direction, maystop moving or may move in a positive direction to maintain the contactforce on the substrate. Once the moving member moves to a position ofabout 1 mm to about 7 mm in a positive (+x) direction from the middleposition (x=0) of the moving member, then the servo-control system mayaccelerate movement of the moving member with the wafer thereon. Forexample, when the position of the moving member is at about 1 mm toabout 7 mm, or about 2 mm in a positive direction from a center positionof the moving member, the servo-control system sends a signal to theproportional pneumatic valve to increase pressure in at least one of thefirst chamber or the second chamber to accelerate the moving member inthe positive direction. According to embodiments, the method can includeaccelerating the moving member to a speed of about 10 mm/s to about 150mm/s, or about 15 mm/s to about 125 mm/s, or about 20 mm/s to about 100mm/s, or about 25 mm/s to about 75 mm/s, or about 30 mm/s to about 50mm/s, or about 30 mm/s to about 35 mm/s, or about 30 mm/s, or about 35mm/s, or about 100 mm/s. It should be noted that although the drawingsin FIGS. 3 and 4 are shown in a horizontal arrangement, lift pinassemblies are typically in a vertical orientation.

According to various embodiments, during processing of the substrate inthe chamber, the at least one lift pin is lowered to a hard stopposition (y=0). Upon completion of processing, the at least one lift pinis moved upward at a velocity of about 1 mm/s to about 3 mm/s, or about2 mm/s to contact the substrate at a substrate release plane (e.g., y=20mm). As described above, the contact force of the at least one lift pinon the substrate is controlled to about 2 N to about 10 N. Once themoving member in the pneumatic actuator and the at least one lift pinwith the substrate thereon move about 2 mm to about 7 mm in a positivedirection from a middle position in the pneumatic actuator, then theservo-control system determines that the substrate is clear of thesupport.

The servo-control system may then accelerate the moving member to avelocity of about 10 mm/s to about 150 mm/s, or about 15 mm/s to about125 mm/s, or about 20 mm/s to about 100 mm/s, or about 25 mm/s to about75 mm/s, or about 30 mm/s to about 50 mm/s, or about 30 mm/s to about 35mm/s, or about 30 mm/s, or about 35 mm/s, or about 100 mm/s. When thesubstrate is at or near a substrate exchange plane (e.g., y=25 mm), thenthe servo-control system may slow the speed of the at least one lift pinand substrate to about 1 mm/s to about 25 mm/s, or about 5 mm/s to about20 mm/s, or about 10 mm/s to about 15 mm/s to softly contact an endeffector of a robot arm with the substrate positioned at a waferexchange plane (e.g., y=25 mm). Once the substrate is securelypositioned on the end effector, the robot arm with the substratereceived thereon may move at a velocity of about 35 mm/s to about 50mm/s to a substrate lift plane (e.g., y=30 mm) and transfer thesubstrate to the transfer chamber. In embodiments, at about 15 mm toabout 50 mm, or about 35 mm above the lowered hard stop, there is anupper hard stop.

According to embodiments, the above described methodology can bereversed. In particular, the robot arm and end effector with a newsubstrate received thereon may be moved from the wafer lift plane to thesubstrate exchange plane at a rate of about 35 mm/s to about 50 mm/s. Atthe wafer exchange plane, the substrate is received by the at least onelift pin which is then lowered at a velocity of about 1 mm/s to about 25mm/s, or about 5 mm/s to about 20 mm/s, or about 10 mm/s to about 15mm/s. Once the substrate and at least one lift pin clear the endeffector, the at least one lift pin is lowered at a velocity of about 10mm/s to about 150 mm/s, or about 15 mm/s to about 125 mm/s, or about 20mm/s to about 100 mm/s, or about 25 mm/s to about 75 mm/s, or about 30mm/s to about 50 mm/s, or about 30 mm/s to about 35 mm/s, or about 30mm/s, or about 35 mm/s, or about 100 mm/s. When the substrate reachesthe support, the velocity is slowed to about 1 mm/s to about 3 mm/s, orabout 2 mm/s to softly place the substrate on the support.

The above described apparatus, systems and methods shorten the range ofmotion of the at least one lift pin when lifting and lowering asubstrate.

The preceding description sets forth numerous specific details such asexamples of specific systems, components, methods, and so forth, inorder to provide a good understanding of several embodiments of thepresent disclosure. It will be apparent to one skilled in the art,however, that at least some embodiments of the present disclosure may bepracticed without these specific details. In other instances, well-knowncomponents or methods are not described in detail or are presented insimple block diagram format in order to avoid unnecessarily obscuringthe present disclosure. Thus, the specific details set forth are merelyexemplary. Particular implementations may vary from these exemplarydetails and still be contemplated to be within the scope of the presentdisclosure.

Although the operations of the methods herein are shown and described ina particular order, the order of the operations of each method may bealtered so that certain operations may be performed in an inverse orderor so that certain operation may be performed, at least in part,concurrently with other operations. In another embodiment, instructionsor sub-operations of distinct operations may be in an intermittentand/or alternating manner.

It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reading and understanding theabove description. The scope of the disclosure should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

I/We claim:
 1. A lift apparatus for transferring a substrate between asupport and a transfer plane, the lift apparatus comprising: a lift pinassembly, comprising: a lift pin configured to move the substratebetween the support and the transfer plane; at least one pneumaticactuator comprising a moving member configured to provide a load to thelift pin; at least one proportional pneumatic valve configured tocontrol fluid flow between the at least one pneumatic actuator and apressurized fluid supply or a vent; a plurality of pressure sensors eachconfigured to independently measure pressure in a respective supply lineto the at least one pneumatic actuator; and at least one position sensorconfigured to measure a position of the member; and a servo-controlsystem in communication with the lift pin assembly.
 2. The liftapparatus of claim 1, wherein the lift apparatus comprises a pluralityof lift pin assemblies.
 3. The lift apparatus of claim 2, wherein theplurality of lift pin assemblies are configured to move the substratebetween the support and the transfer plane.
 4. The lift apparatus ofclaim 2, wherein the servo-control system is in communication with theplurality of lift pin assemblies.
 5. The lift apparatus of claim 4,wherein the servo-control system is configured to maintain a closedloop, wherein at least one of chamber pressure or moving member positionis controlled within the at least one pneumatic actuator.
 6. The liftapparatus of claim 4, wherein the at least one proportional pneumaticvalve is configured to direct pressurized fluid to at least one of theplurality of chambers in response to a control signal from theservo-control system.
 7. The lift apparatus of claim 1, wherein the atleast one pneumatic actuator comprises a plurality of chambers, eachchamber connected to the respective supply line measured by a respectiveone of the plurality of pressure sensors.
 8. The lift apparatus of claim1, comprising a plurality of proportional pneumatic valves configured totransport fluid between the at least one pneumatic actuator and thepressurized fluid supply or the vent.
 9. The lift apparatus of claim 1,wherein the servo control system comprises a controller attached to theat least one pneumatic actuator, the plurality of pressure sensors, theat least one position sensor and the at least one proportional pneumaticvalve.
 10. A method, comprising: receiving by a controller a firstpressure measurement from a first pressure sensor that measures pressurein a first chamber of a pneumatic actuator; receiving by the controllera second pressure measurement from a second pressure sensor thatmeasures pressure in a second chamber of the pneumatic actuator;receiving by the controller a position measurement from a positionsensor that measures a position of a moving member of the pneumaticactuator; generating a control signal based on the first pressuremeasurement, the second pressure measurement and the positionmeasurement; transmitting the control signal to at least oneproportional pneumatic valve of a servo-control system to controlpressurized fluid to the pneumatic actuator; and operating theservo-control system to extend at least one lift pin and lift asubstrate off of a support via the at least one lift pin.
 11. The methodof claim 10, further comprising transferring the substrate from the atleast one lift pin to a transfer chamber using a robot arm.
 12. Themethod of claim 10, wherein the controller determines the differencebetween the first pressure measurement and the second pressuremeasurement to determine an output force of the pneumatic actuator, andwherein the controller adds the first pressure measurement to the secondpressure measurement to determine a stiffness of the pneumatic actuator.13. The method of claim 12, wherein in response to the output force, thestiffness and the position of the moving member, the controller controlsthe at least one proportional pneumatic valve by determining a pressurefor each of two chambers of the pneumatic actuator.
 14. A methodcomprising: operating a servo-control system to lift a substrate off ofa substrate support, wherein the servo-control system is configured tocontrol a lift pin assembly for lifting the substrate, comprising:actuating at least one proportional pneumatic valve to permit gas toflow through a first gas line into a first chamber of a pneumaticactuator of the lift pin assembly and through a second gas line into asecond chamber of the pneumatic actuator; measuring pressure in thefirst gas line with a first pressure sensor and measuring pressure inthe second gas line with a second pressure sensor; measuring position ofa moving member of the pneumatic actuator with a position sensor;controlling the at least one proportional pneumatic valve with theservo-control system to apply a contact force of about 2 N to about 10 Nby the moving member to the substrate; and lifting the substrate off ofthe support by a lift pin operable to receive a load by the movingmember.
 15. The method of claim 14, wherein the lift pin assemblycomprises: the lift pin; the pneumatic actuator comprising the movingmember, the at least one proportional pneumatic valve; the firstpressure sensor; the second pressure sensor, and the position sensor.16. The method of claim 14, wherein a controller of the servo-controlsystem is connected to the pneumatic actuator, the at least oneproportional pneumatic valve, the plurality of pressure sensors and theposition sensor.
 17. The method of claim 14, wherein controlling the atleast one proportional pneumatic valve comprises maintaining, reducingor reversing gas flow to at least one of the first chamber or the secondchamber.
 18. The method of claim 14, wherein controlling the at leastone proportional pneumatic valve comprises maintaining pressure to thefirst chamber and the second chamber at a constant value to apply aconstant contact force by the moving member to the substrate.
 19. Themethod of claim 14, wherein when the position of the moving member is atabout 1 mm to about 7 mm, or about 2 mm in a positive direction from acenter position of the moving member, the servo-control system sends asignal to the proportional pneumatic valve to increase pressure in atleast one of the first chamber or the second chamber to accelerate themoving member in the positive direction.
 20. The method of claim 19,wherein the moving member is accelerated to a speed of about 50 mm/s toabout 150 mm/s, or about 75 mm/s to about 125 mm/s, or about 100 mm/s.